1. Field of the Invention
The invention relates to a method of operation for a claw-type vacuum pump with two or more stages, each of which has a suction chamber with a pair of claw rotors and end-located suction and discharge ports. Moreover, the invention relates to a claw-type vacuum pump suitable for carrying out this method of operation.
2. Discussion of the Related Art
A claw-type vacuum pump is known from EU-A 365 695. Each rotor of the rotor pairs is equipped with a claw (tooth) and a recess respectively. They rotate comb-like in the suction chamber without coming in to contact. During the synchronous motion the rotors at first create spaces which increase in volume, after which the volume of these spaces is reduced, whereby these spaces displace the gas flowing in at the suction side to the pressure side. It is the task of the claws to separate the suction side from the pressure side. For this, the peripheral surface areas of the claws form the necessary sealing gaps together with the peripheral inside wall of the suction chamber. During the combing pass of the recessed areas of the claws through the central area of the suction chamber (pass-through phase), the claws are not able to fulfill their task of separating the suction side from the pressure side, because during this phase they are no longer moving close to the peripheral inside wall of the suction chamber. During this phase it is therefore required to ensure that suction side and pressure side are separated by closing the suction port or the discharge port--or both. This is done by the rotors themselves in a known manner. The suction and discharge ports are arranged and designed at the end-location in such a way that they can be opened or closed with the aid of the recesses in the rotors.